Open Port Checker

Test whether specific TCP ports are open or closed on a remote host. Enter a hostname or IP address and select ports to check.

How It Works

This tool attempts to establish a WebSocket connection to the specified host on each selected port. Based on the browser's response, the tool determines whether a port is likely open, closed, or filtered:

• Open: The connection attempt receives a response (even a rejection) from the target port, indicating a service is listening. The connection itself is immediately closed after detection.
• Closed: The connection is actively refused by the remote host, typically indicated by a TCP RST (reset) packet. This means no service is listening on that port.
• Filtered: No response is received within the timeout period. This usually means a firewall is silently dropping the packets, preventing the scanner from determining whether the port is open or closed.

Understanding Port States

Network ports can be in three general states:

• Open: A service is actively accepting connections. This is normal for web servers (port 80/443), mail servers (port 25/587), and other network services. However, unnecessary open ports can be security risks.
• Closed: No service is listening, but the port is reachable. The host actively rejects connection attempts. This confirms the host is online but no application is bound to that port.
• Filtered: A firewall or security device is blocking access to the port. Packets are silently dropped with no response sent back. This is a common security measure to hide services from port scanners.

Common Ports and Services

Security Considerations

• Only scan hosts you own or have explicit permission to test
• Unauthorized port scanning may violate terms of service or local laws
• Open ports should be regularly audited and unnecessary services disabled
• Use firewalls to restrict access to only required ports

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